The present invention relates generally to teletext type communications systems and, more particularly, to improvements in the video displays produced by such systems.
Teletext is a generic term for a new and rapidly growing television based communications technique which uses the vertical blanking interval of a broadcast television signal for transmission of text and graphics information. Systems implementing this technique are presently operational in various countries, such as in England where teletext formatted text and graphics material is transmitted in digitally encoded form on lines 17, 18, 330 and 331 of their 625 line system. Television receivers equipped with teletext decoders process the transmitted data for forming a display on a CRT of the text and graphics information. The teletext decoder conventionally includes means for acquiring and storing a selected page of transmitted teletext data, the stored teletext encoded information being applied to a display generator for synthesizing R, G, B video character signals suitable for driving the CRT of the television receiver for producing a display reflecting the stored data. In addition, a so-called Y signal is developed by the teletext decoder to facilitate a mixed mode operation of the television receiver wherein the teletext characters are superimposed on the CRT screen over the normal video image produced in response to the broadcast television signal. In order to accomplish the foregoing, the Y signal assumes a first logic state in time coincidence with the development of a R, G or B teletext character signal (sometimes referred to as a foreground portions of the display) and otherwise assumes a second logic state, (i.e., during background portions of the display.
The video image display produced on the CRT of a television receiver in response to a conventional teletext decoder has been found to have certain undesirable limitations. For example, a blue foreground text/graphics characters cannot be displayed on a blue background since both are produced at the same intensity and are therefore indistinguishable from each other. In addition, foreground text/graphics characters when displayed in certain colors to which the human eye is relatively insensitive, e.g., red and blue, are extremely difficult to read.
It is, therefore, a basic object of the present invention to provide a technique for improving the video image display produced on the CRT of a television receiver in response to a conventional teletext-type decoder.
It is a more specific object of the invention to provide a technique for improving the video image display produced on the CRT of a television receiver in response to a conventional teletext-type decoder by displaying the foreground text/graphics characters at a different intensity level than the background portions of the display.
It is a further object of the invention to provide a technique for improving the video image display produced on the CRT of a television receiver in response to a conventional teletext type decoder by increasing the relative intensity of the text/graphics characters displayed in selected colors.